The present invention generally relates to a device for monitoring the liquid level in a tank and more particularly to an arrangement for accurately installing a replaceable reed switch of the monitoring device.
The problem with devices for monitoring the liquid level of a tank is that the associated reed switch must be inserted with its electrical contact terminal into the interior of a hollow tube so is to fit as accurately as possible as an independent exchangeable part once securely fixed in place.
Additionally, structural measures are necessary to ensure installation of the reed switch in the correct circumferential position and also to ensure simultaneously that the electrical contacts of the reed switch are always poled in a predetermined manner when a plug is applied. Furthermore, accidental detachment of the reed switch in the installed state should be reliably prevented.
Accordingly, it is an object of the present invention to provide a device for monitoring the liquid level in a tank in which the installation and accurate fit of the exchangeably insertable reed switch is provided.
In accordance with preferred embodiments of the present invention, a centric alignment of a slide-in part, carrying the reed switch, inside the cylindrical interior of a hollow rod is ensured at all times by three resilient abutment zones distributed uniformly around the circumference of the slide-in part.
Centering bushings having a likewise resilient three-point support within a receiving bore are disclosed by German Published Unexamined Patent Application 3,328,514 AL. However, the object of these bushings is solely to keep the diameter of the bushing aperture as centric as possible and unchanged in size in the case of an inaccurately fitted or stepped receiving bore. The arrangement further permits compensation of dimensional deviations between the parts to be connected to each other, which exist relative to connecting parts to be introduced and may be cumulative.
The compensation of such dimensional deviations is not necessary in preferred embodiments of the present invention where the accurate fit on the slide-in part inside the hollow rod is realized, because the slide-in part is freely introducible into the hollow rod.
However, it is important for preferred embodiments of present invention to obtain an accurate fit of the slide-in part, free from play, utilizing the simplest possible assembly facility to provide a centric securing of the slide-in part inside the hollow rod with a firm tensioning.
Guide grooves provided inside the cylindrical inner envelope surface of the hollow rod according to one embodiment of the present invention permit a firm tensioning of the slide-in part inside the hollow rod. The guide grooves, which correspond to the number of the resilient abutment zones of the slide-in part and are distributed around the circumference in the same manner, permit an extremely convenient introduction of the slide-in part with the reed switch present inside it.
The final tensioning of the slide-in part at the resilient abutment zones only occurs in a second step after the introduction of the slide-in part into the hollow rod, by a rotation of the slide-in part The rotation causes the resilient abutment zones of the slide-in part to be located in regions circumferentially between the guide grooves of the inner envelope of the hollow rod. Due to the guide grooves, it is possible to provide a degree of tensioning of the final assembled device which would be virtually impossible during the introduction of the slide-in part into the hollow manually. The guide grooves therefore contribute to a high degree to the desired accurate and firm fit of the slide-in part inside the hollow rod which is achieved during assembly with truly simple means and the exertion of little force.
Fastening means are also provided which provide a circumferentially and radially definite secure fixing of the reed switch carrying slide-in part.
Rotational security for the slide-in part can be achieved in a very simple and absolutely reliable manner by an adaptation of the form of an electrical plug to be applied on the electrical contacts of the reed switch to a given form of the hollow rod and/or of a foot region of the slide-in part.
In the case of a tongue and groove connection by which the plug for the current to be conducted to the reed switch is anchored on the hollow rod and/or the slide-in element, a predetermined poling of the plug relative to the contacts of the reed switch can be ensured additionally by an appropriate conformation.
A bayonet fastening, by which the anchorage of the slide-in part with the reed switch inside the hollow rod is effected, can also be designed with regard to its interlacing parts so that the slide-in part is introducible into the hollow rod only in a circumferentially predetermined position.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.